As an example of a casing assembly required to have the foregoing performance, as shown in FIG. 20, a connector casing E′ for housing a microcomputer for controlling a vehicle engine or the like, or various electric·electronic equipments can be cited. This connector casing E′ is fitted in an engine room or a vehicle compartment, and is used to control the operation of an engine or to control various driving devices of the vehicle. In order to maintain the control to be accurately carried out without an erroneous operation, that is, in order to always accurately and stably operate the housed microcomputer or various electric·electronic equipment, it is necessary to prevent water droplets or dust etc. from entering the connector casing E′.
In order to satisfy such a request, for example, if the connector casing is completely sealed hermetically, the object of preventing the water droplet, the dust etc., or the like from entering is achieved. However, heat is generated at the time of operation of the inner microcomputer or various electric·electronic equipment, and the air in the connector is heated and expanded by this heat generation. As a result, the pressure in the casing becomes high, and there is a case where a sealed portion of the casing is partially broken. Further, because of the temperature rise due to the heat generation, there is a danger that an erroneous operation will occur in the equipment such as the inner computer, or a deterioration in performance will be caused.
In order to solve such problems, an article in which a vent hole H0′ is formed at a part of a cover 2′ of the connector casing E′ is known. A gas permeable sheet S′ which permits a variety of gases, such as air, and moisture in the air to permeate through and prevents water drops from permeating through, is attached so as to close this vent hole H0′.
The cover 2′ of this connector casing E′ is molded by injection molding of a synthetic resin so as to have the vent hole H0′. After the molding, the permeable sheet S′ is disposed to close the vent hole H0′, and is attached by bonding using an adhesive·bonding agent formed into a doughnut shape, a double faced pressure sensitive adhesive tape 91 or the like. Incidentally, in FIG. 14, reference numeral 92 designates a base member laminated on the thin film permeable sheet S′ for reinforcement so that it can be easily handled.
By the foregoing method, in the case where the permeable sheet S′ is bonded to the vent hole H0′ of the connector casing E′, there have been the following problems. (1) Since the permeable sheet not smaller than the size of the vent hole is exposed to the outside, an external object is apt to unexpectedly come in direct contact with the permeable sheet during its handling, using, maintenance, or the like. When a force exceeding a limit is applied as a result of the contact, this permeable sheet is damaged. For example, there is a danger that a pointed end of a screw driver will tear the permeable sheet carelessly to make a hole. (2) It is necessary to carry out the bonding of the permeable sheet by a different step from a molding step of the casing. Since there is a fear that the permeable sheet will be damaged during this bonding operation, excessive attentiveness is required for the bonding operation of the permeable sheet. (3) Since a bonding force is apt to vary by a variation in the amount of adhesive used, or the press force of the permeable sheet, a uniform and stable bonding state is hard to obtain over the whole bonded portion.
An object of the invention is to provide a casing member in which even if an external object is going to come in contact with a permeable sheet by carelessness or the like, a probability that the object comes in direct contact with the permeable sheet is lowered, and there is little danger that the permeable sheet is damaged, and to provide its efficient manufacturing method.